This project addresses issues in the thrombogenic pathways that have yet to be resolved. First, is the role of vascular endothelial surface microdomain context in the association of Tissue Factor (TF) with its substrates factors X and IX? This is being addressed in a novel manner with creation of various Selective Vascular Thrombogens that dock to different endothelial surface context and can be observed in vivo by real-time intravital microscopy as well as in in vitro cell assays and animal models of TF driven thrombosis and disseminated intravascular coagulation. Coupled with advanced imaging methods at the molecular level, use of genetically modified mice, and the collaboration with Project 2 to explore the differences in cell signaling, with Project 3 to explore the context in various genetically modified mice including high human TF expressing mice, and with Project 4 to approach the full three dimensional protein interactions coupled with the predicted atomic level interactions, a new level of data and insight will be forthcoming. Advancing initial discovery of a small constrained peptidyl ligand for a key interactive protein surface locus involved in association of the factor X with the functional TF:VIIa we will be able for the first time to selectively inhibit the extrinsic limb of the coagulation/thrombogenic pathway without inhibiting factor IX activation and effecting the intrinsic limb of the coagulation hemostatic pathways. This will require collaboration with all projects and cores for its execution. This set of studies will also address the correct molecular identification by mass spectrometry of the real endothelial surface factor Xa specific receptor. This is currently in process and potential candidate molecules have been identified and bear no relationship to the current scientific content of the literature. How important this receptor, FXaR, may be in thrombogenic and hemostatic pathways will be explored as well as its structure and basis of function. We have established by independent search methods a set of 92 peptidyl probes selective for the arterial atherosclerotic plaque surface endothelium. We have completed identification of one of the targets and are advancing three others to protein identification. The initially solved target that is very selective in vivo in atherosclerotic ApoE knockout mice is also similarly expressed on the surface of human iliac artery atherosclerotic plaques ex vivo. We will assess the linkage between plaque expression of these panels of markers and the histology, human TF content in the huTF knockin mouse/TF knockout mice as well as explore foam cell content and other possible markers of thrombotic risk of plaques. Such data and the probes may provide the much lacking means of in vivo imaging of the vasculature of humans for identification of the high risk 'susceptible' plaques.